A threefold objective of this research is to determine (1) The dose relationship of lead to physiopathologic effects in pigs, a species physiologically similar to man, (2) The influence of subclinical lead exposure on resistance to infectious agents, and (3) The mechanism for lead-mediated supression of resistance to infectious agents. Lead acetate has been given daily to groups of pigs for 90-day periods to establish toxicity and immune response effects. Subsequent experimentation has included the exposure of pigs to subclinical levels of lead for up to 30 days followed by exposure of the animals to bacterial agents of known virulence. The effect of lead exposure upon resistance to the infectious agents is being evaluated using death, immunologic changes, and histopathologic parameters. This data will be evaluated in relation to dosage and tissue residue levels of lead. Studies similar to those in swine are also being conducted in mice and hamsters.